Add back activesupport

We are not ready to remove it. There are instances of `blank?` and
`singularize` that are used in the code.

Removing `activesupport` still not fails any of the tests, as we have
`generator_spec` that uses and installs `activesupport`.

README.md

@@ -9,8 +9,6 @@
 
 LightService is a powerful and flexible service skeleton framework with an emphasis on simplicity
 
-🔥 **It now comes with no external gem dependency.** 🔥
-
 ## Table of Contents
 - [Table of Contents](#table-of-contents)
 - [Why LightService?](#why-lightservice)

light-service.gemspec

@@ -17,6 +17,8 @@ Gem::Specification.new do |gem|
   gem.version       = LightService::VERSION
   gem.required_ruby_version = '>= 2.6.0'
 
+  gem.add_dependency("activesupport", "~> 7.0") # We still need this
+
   gem.add_development_dependency("generator_spec", "~> 0.9.4")
   gem.add_development_dependency("test-unit", "~> 3.0") # Needed for generator specs.
   gem.add_development_dependency("rspec", "~> 3.0")